An uplink multi-user multiple-input multiple-output (MU-MIMO) system is a virtual MIMO system where each terminal constituting the multi-user MIMO system transmits a data stream, but the data streams transmitted from the terminals occupy the same time and frequency resource, and thus from the perspective of a receiver, these data streams from the different terminals can be regarded as data streams from different antennas on the same terminal, thereby constituting an MIMO system with an improved capacity.
LTE-A evolving from LTE is directed toward higher data transmission efficiency and spectrum utilization efficiency. In order to further improve the rate of an edge user and the overall performance of a system, the coordinated multipoint transmission (CoMP) has been incorporated by the third generation partner project (3GPP) into the architecture of LTE-A. CoMP designed generally for an edge user refers to coordinated transmission and reception of data for one or more users through geographically separate transmission points, thereby improving the transmission efficiency and performance at the edge of a cell.
The architecture of CoMP differs from a network architecture of existing LTE R8 in that there are a plurality of geographically separate transmission points serving an edge user in the CoMP architecture, and a central or edge user is served only by a cell where the central or edge user is located in a traditional cellular network architecture of LTE R8. Therefore in the latter case, only a base station serving the user receives uplink data of the user in the uplink path, while in the CoMP architecture, the plurality of transmission points receive the uplink data from the user during uplink transmission.
Among coordinated transmission cells, the cells serving concurrently a user equipment (UE) form a cooperating set including a primary cell responsible for tasks of resource scheduling and allocation, coordinated data processing, etc., and one or more cooperative cells responsible for only the process of transmitting and receiving data.
The conventional coordinated multipoint transmission/reception includes intra-eNodeB (evolved NodeB) cooperation and inter-eNodeB cooperation. In a CoMP scenario of intra-eNodeB cooperation, a plurality of cells under the control of an eNodeB serve the same user, and a transmission point of each cell only has radio frequency function. Each cell transmits uplink data directly to the eNodeB for processing over a dedicated physical link upon reception of the uplink data. In a CoMP scenario of inter-eNodeB cooperation, a plurality of cells under the control of different eNodeBs serve the same user, and one of the eNodeBs is selected as a master eNodeB responsible for control operations of resource allocation and scheduling, etc. Upon reception of uplink data, a cooperative eNodeB transmits the preliminarily processed data to the master eNodeB, and the master eNodeB completes the processing of the data. Interaction of data, control, etc., is transmitted between the eNodeBs via an X2 interface.
In LTE Release 8 supporting the uplink multi-user MIMO (MU-MIMO), a user simply transmits data to a serving cell and a paired user is selected by a base station in the serving cell. According to the optimum principle of selecting a paired user, interference between the paired users is minimized, that is, channels relating to the paired users shall be orthogonal channels. As illustrated in FIG. 1, there are a number Nr of antennas for reception in a cell C1 and a number Nt of antennas for transmission from users U1 and U2, and there is an uplink channel H1 between the cell C1 and the user U1 and an uplink channel H2 between the C1 and the user U2. H1 and H2 represent a matrix having the dimension of Nr×Nt. In order to minimize interference between the users U1 and U2, the channels H1 and H relating to the users U1 and U2 have to be orthogonal as shown in Formula 1:∥H1H2H∥≈0  Formula 1
where the superscript “H” represents conjugated transposition of a matrix, and ∥A∥ represents the norm of the matrix A.
Under the CoMP scenario, a user equipment (UE) is served by one or more cells through the same time and frequency resource, and a CoMP-MU-MIMO transmission solution arises when a plurality of users are served by a plurality of cells through the same time and frequency resource. Due to concurrent presence of the CoMP scenario and the traditional single-cell service scenario in LTE-A, there are a plurality of MU-MIMO pairing types, and a conventional user pairing process does not support multi-user MIMO under a CoMP scenario, thus resulting in a need of proposing a solution of pairing users for the uplink multi-user MIMO system under CoMP scenario.